How much work is done in J?

Question

Four railroad cars, each of mass 2.15 X10^4 kg, are coupled together and coasting along horizontal tracks at speed vi toward the south. A very strong but foolish movie actor riding on the second car uncouples the front car and gives it a big push, increasing its speed to 4.35 m/s south. The remaining three cars continue moving south, now at 2.40 m/s.

The inital speed of the cars is 2.89 m/s
How much work did the actor do in J?

Answer 1

Find the difference in Kinetic Energy...

1/2 M *(v1^2 - v2^2)
=================================
Car1 = 113637.8 J
Car2-4 = 27865.075/car = 83595.225

BTW the speed of the first car should be 4.36m/s